The term "manbasket" as used herein encompasses various types of industrial personnel platforms, including man-cages and the like, used to elevate personnel and equipment to reach high, otherwise inaccessible locations. For safety reasons, a manbasket is typically at least partially enclosed circumferentially, and sometimes also overhead, to prevent personnel from falling off the platform.
Although manbaskets can be elevated using any of several types of lifting means, such as cranes and jacks, a convenient way to elevate a manbasket is by employing a forklift vehicle. Forklifts as generally known in the art are self-propelled vehicles having a lifting fork usually on the front end thereof which is used to lift goods-loaded pallets and other heavy or bulky items for transportation to remote locations or for movement from one elevation to another. A typical lifting fork has two outwardly projecting parallel tines. The lifting fork is mounted on a substantially vertical track, or "mast", on the vehicle. The mast is equipped with a winch or analogous mechanism used to raise or lower the fork relative to the vehicle.
To elevate a manbasket using a forklift, the tines of the lifting fork are typically placed beneath the platform portion of the manbasket, the platform serving as the "floor" of the manbasket. Some manbaskets are provided with grooves or channels beneath the platform to ensure that the tines are placed properly relative to the mass of the manbasket and to prevent the manbasket from sliding laterally off the tines.
Many forklifts are equipped with means for adjusting the forward and rearward tilt of the mast which, in turn, adjusts the tilt of the tines from horizontal. Adjusting the fork so that the tines are angled downward relative to horizontal can pose a substantial hazard to personnel in a manbasket supported by the fork in that the manbasket can slide in a forward direction off the fork. Even if the tines are not angled downward, it is possible for a manbasket to slip forward off the fork if a forward-moving forklift vehicle carrying the manbasket stops suddenly or the personnel in the manbasket cause the manbasket to shift position on the tines as a result of shifts of weight or exertions by the personnel therein. Sliding of the manbasket on the tines in a rearward direction does not pose as great a risk since such movement tends to place the manbasket more completely on the tines. Also, excessive rearward movement of the manbasket on the tines is usually obstructed by the mast and by various abutting plates or bars situated behind and above the tines.
Several methods and apparatuses are known in the art for securing large objects such as manbaskets and the like to the tines of a forklift. For example, U.S. Pat. No. 3,889,833 to Thomas discloses plural manually pivotable "square Z" latches provided on the manbasket for engaging the abutting plate of the forklift. A disadvantage of such latches is that they are usable only with a forklift having an abutting plate with the proper depth and located the proper distance above the tines. Also, such latches are biased by gravity to return to the latched position, which is not fail-safe. For example, if the latch journal fails to allow free rotation of the latch due to rust or incursion of dirt, the latch may not engage the abutting plate, particularly if one forgets to manually engage the latch. Another disadvantage is that the latches must be manually opened, which can be inconvenient.
U.S. Pat. No. 3,101,128 to Dane discloses a personnel platform provided with sets of parallel channels adapted for receiving the tines of the lifting fork therebetween. Each set of channels has an opening into which a tine is inserted. Each opening is partially obstructed with a vertical plate adapted to become situated behind the heel of the tine whenever the manbasket is lifted off the ground by the lifting fork. Unfortunately, providing such a feature requires that the manbasket rest in a tilted orientation on the ground to allow insertion of the tines. Also, the manbasket is provided with an inwardly tilting side panel to permit incursion of the forklift mast between two lateral sides of the manbasket. Hence, Dane discloses an elaborate mechanical interconnection between the tilting side panel and a pair of swingable legs which keep the manbasket in a tilted position on the ground. The fact that the manbasket must remain tilted on the ground is disadvantageous because workers are discomforted thereby. Also, the tilted floor can make it difficult to stabilize equipment and tools placed in the manbasket until the manbasket is elevated by the forklift. Also, proper placement of the manbasket on the tines requires appreciable manual intervention, including moving the tilted side panel into a vertical position after the manbasket has been lifted off the ground.
Another means known in the art for securing a manbasket to a lifting fork includes a chain passed around the mast and fastened to the manbasket. A disadvantage of this method is that it is easy to forget or ignore fastening the chain.
Another means known in the art is to fasten the manbasket to the tines using pins or screws or the like. This method has the disadvantage in that pins or screws must be manually engaged against the tines before elevating the manbasket and manually released when the manbasket is not in use. Also, screws are vulnerable to damage by the tines. For example, U.S. Pat. No. 4,049,146 to Decker discloses a screw mechanism which could be adapted for use with a manbasket.
Hence, there is a need for an apparatus and method for securing a manbasket to a lifting fork on a forklift vehicle, the apparatus and method characterized by automatic operation requiring no deliberate action by personnel to engage the securing means before the manbasket is elevated.
There is also a need for such an apparatus and method which reliably secure an elevated manbasket containing personnel and equipment to the tines of said lifting fork to prevent the manbasket from slipping forward off the tines.
There is also a need for such an apparatus and method which allow the floor of the manbasket to remain horizontal when the manbasket is resting upright on the ground.
There is also a need for such an apparatus and method wherein the tines of the lifting fork are automatically positioned properly relative to the manbasket for elevating the manbasket without causing a material imbalance in the resulting load supported by the tines.
There is also a need for such an apparatus and method that automatically disengage the tines from the manbasket whenever the manbasket is resting in an upright position on the ground or other reference surface.
There is also a need for such an apparatus and method that can be used to secure a manbasket to forks of different makes and models of forklift vehicles without the need for intervening adaptive action.